JP2006086218A - Ridge type semiconductor laser device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ridge type semiconductor laser device which has no large irregularity other than peaks in a far field pattern in a horizontal lateral mode and therefore can be APC-driven stably while at the same time can be suppressed for an increase in manufacturing cost, and to provide its manufacturing method. <P>SOLUTION: The ridge type semiconductor laser device 100 comprises at least an n-type clad layer 103, an active layer 104, a p-type clad layer 105, and a ridge 107, which are stacked in this order. The side faces of the ridge 107 and the top face of the p-type clad layer 105 are coated with an insulation film 108. The insulation film 108 consists of an insulation film whose refractive index is smaller than that of the p-type clad layer 105, and the difference in both of the refractive indexes are within 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ridge type semiconductor laser element used for a light source for reading and writing on an optical disk and a method for manufacturing the same.

A conventional ridge type semiconductor laser device has a structure as shown in FIG. That is, an N-type GaAs buffer layer 102, an N-type cladding layer 103 made of N-type Al _0.5 Ga _0.5 As, an active layer 104 made of Al _0.13 Ga _0.87 As, and a P-type Al layer on a substrate 101 made of N-type GaAs. A P-type cladding layer 105 made of _0.5 Ga _0.5 As and having a ridge 107 protruding upward is sequentially laminated. A cap layer 106 made of P-type GaAs is disposed on the ridge 107, and the refractive index difference between the ridge 107 and both sides of the ridge 107 and the P-type cladding layer 105 is different from that of the P-type cladding layer 105. It is covered with an insulating film 108 such as silicon oxide or silicon nitride. Further, a P-side ohmic electrode 110 made of, for example, Au—Zn or the like is formed on the cap layer 106, and Au is formed on the P-side ohmic electrode 110 and outside the insulating film 108. A die bond electrode 111 is formed. An N-side ohmic electrode 112 made of, for example, Au—Ge is formed under the substrate 101 made of N-type GaAs, and a wire bond electrode 113 made of Au is formed thereunder.

  In the above ridge type semiconductor laser element, an AlGaAs mixed crystal is used for the active layer 104, but a ridge type semiconductor laser element using an AlGaInP mixed crystal for the active layer 104 is also manufactured.

In the ridge type semiconductor laser device having the above structure, due to the above structure, the large refractive index region 104a which is the portion of the active layer 104 in contact with the ridge portion 107 through the P type cladding layer 105, and the P type cladding layer A refractive index difference from the small refractive index region 104b, which is the portion of the active layer 104 in contact with the insulating film 108 via 105, is generated, and the optical confinement in the lateral direction can be made possible by this refractive index difference. Therefore, this ridge type semiconductor laser element is widely used, and various improvements regarding this ridge type semiconductor laser element have been proposed (see, for example, Patent Documents 1 to 3).
JP 09-051146 A JP 2003-46197 A JP 2003-51643 A

   The above conventional ridge type semiconductor laser device has the following problems.

  The insulating film 108 made of silicon oxide, silicon nitride, or the like formed on the side surface of the ridge 107 made of P-type AlGaAs and the upper surface of the P-type AlGaAs cladding layer 105 has a smaller refractive index than the P-type AlGaAs cladding layer 105. Therefore, the portion of the active layer 104 that contacts the ridge 107 via the P-type cladding layer 105 (large refractive index region 104a) and the portion of the active layer 104 that contacts the insulating film 108 via the P-type cladding layer 105 (small refraction). A difference in refractive index from the index region 104b) occurs. That is, the boundary between the large refractive index region 104a and the small refractive index region 104b has a refractive index difference. At the same time, the ridge 107 serves as a current path for current confinement by the insulating film 108. The side surface of the ridge portion 107 of the manufactured ridge type semiconductor laser element is in a state in which an uneven portion is formed.

  In such a conventional ridge-type semiconductor laser device, the transverse mode (horizontal transverse mode) in the direction parallel to the active layer 104 of the laser light is reflected by the above-mentioned boundary having a difference in refractive index. Since the light is reflected in a state close to total reflection on the surface, it is confined in the ridge 107, and the degree of this confinement largely depends on the above refractive index difference.

  When this difference in refractive index is large, in the horizontal transverse mode of the ridge-type semiconductor laser element, the total reflection critical angle at the concavo-convex portion on the side surface of the ridge portion 107 is exceeded, and the insulating film 108 comes out from the concavo-convex portion on the side surface of the ridge portion 107. As shown in FIGS. 3A and 3B, the far field pattern of the laser beam emitted by the interference between the laser beam and the laser beam emitted from the reflecting surface is other than the peak portion. Severe unevenness may be seen. As shown in FIG. 2, the far field pattern is a measurement of the intensity distribution of the laser beam 121 at a location away from the laser resonator (laser element 100). , Converted into an angle and displayed.

  In the semiconductor laser, in order to control the light output, the light output of the emitted laser light is monitored by a light receiving element to perform constant power output (APC) driving of the semiconductor laser. When the field pattern is severely uneven, normal APC driving cannot be performed, and thus an optical disk apparatus or the like using such a semiconductor laser causes a writing failure or reading failure, and the pickup function of the optical disk apparatus or the like is impaired. It will be.

  As a method of quantitatively evaluating the unevenness of this far field pattern, a numerical value obtained by dividing the difference between the far field pattern and the approximate value obtained by Gaussian fitting by the peak value can be used, and this value is referred to as a ripple value. Called. If this ripple value is 10% or less, the semiconductor laser can be APC driven almost stably.

  FIG. 3A shows the ridge in the case where the insulating film 108 formed on the P-type AlGaAs cladding layer 105 is formed of silicon oxide having a refractive index of 1.5 in the conventional ridge-type semiconductor laser device. 2 shows a horizontal field mode far field pattern in a type semiconductor laser device. As shown in FIG. 3 (a), the far field pattern has large irregularities. The ripple value in this far field pattern was 23%.

  FIG. 3B shows a horizontal field mode far field pattern in a ridge type semiconductor laser device in which the insulating film 108 is formed of silicon nitride having a refractive index of 2.0. Also in this case, as in FIG. 3A, it can be seen that severe unevenness other than the peak portion is generated in the far field pattern. The ripple value in this far field pattern was 15%.

  As described above, in the conventional ridge type semiconductor laser element, the refractive index of the insulating film 108 formed of silicon oxide or silicon nitride is generally too small with respect to the refractive index of the P-type AlGaAs cladding layer 105. When the horizontal transverse mode is confined by the ridge type semiconductor laser element having the insulating film 108 formed of silicon oxide, silicon nitride, or the like, as described above, severe unevenness other than the peak portion occurs in the far field pattern. It was an obstacle for performing easy and stable APC driving.

  In order to solve this problem, there is a method in which instead of the insulating film 108 formed of silicon oxide or silicon nitride, AlGaAs having a composition different from that of the P-type AlGaAs cladding layer 105 is used to form a layer that replaces the insulating film 108. is there. By using this method, the horizontal transverse mode can be confined so that this layer has a refractive index difference with the P-type AlGaAs cladding layer 105. However, in this method, after the ridge portion 107 is formed, a layer in place of the insulating film 108 is formed by using the MOCVD method (metal organic chemical vapor deposition method) or the like. There was a problem that the cost increased.

  Therefore, the present invention has been made to solve such a problem, and there is no intense unevenness other than the peak portion in the far-field pattern in the horizontal and transverse modes, and therefore, stable APC driving is possible. Moreover, it is an object of the present invention to provide a ridge type semiconductor laser device and a method for manufacturing the same that can suppress an increase in manufacturing cost.

  In the ridge-type semiconductor laser device of the present invention, at least an N-type cladding layer, an active layer, and a P-type cladding layer are sequentially stacked from the bottom to the top, and a part of the P-type cladding layer protrudes upward from the P-type cladding layer. The ridge-type semiconductor laser device has a structure in which the ridge portion having the above-described shape is formed and the side surface of the ridge portion and the upper surface of the P-type cladding layer where the ridge portion is not formed are covered with an insulating film. In this ridge type semiconductor laser device, a large refractive index region which is a portion of an active layer in contact with a ridge portion through a P-type cladding layer and a small refraction in which a portion of the active layer is in contact with an insulating film through a P-type cladding layer. A refractive index difference with respect to the refractive index is brought about by the above structure, and the optical confinement in the lateral direction is made by the refractive index difference. In this ridge type semiconductor laser device, the refractive index of the insulating film is smaller than the refractive index of the P-type cladding layer, and the difference between the refractive index of the insulating film and the refractive index of the P-type cladding layer is within one. It is characterized by being.

  In the above ridge type semiconductor laser element, the refractive index of the insulating film is smaller than the refractive index of the P-type cladding layer, and the difference between the refractive index of the insulating film and the refractive index of the P-type cladding layer is within one. In the far field pattern of this ridge type semiconductor laser element, no severe irregularities other than the peak portion are observed. Therefore, the ridge type semiconductor laser element described above is configured using an insulating film that can be stably driven by APC and can be formed at a low cost, and allows crystal growth to be performed again using the MOCVD method or the like. Therefore, an increase in manufacturing cost can be suppressed.

  In the above ridge type semiconductor laser device, the active layer may be formed of an AlGaAs mixed crystal and the refractive index of the insulating film may be 2.4 to 3.4. Alternatively, the active layer may be formed of an AlGaInP mixed crystal, and the refractive index of the insulating film may be 2.3 to 3.3. By doing so, a ridge type that is smaller than the refractive index of the P-type cladding layer, the difference is 1 or less, and realizes a ripple value of 10% or less necessary for stable APC driving of the semiconductor laser. A semiconductor laser element can be realized.

  In the ridge type semiconductor laser device, the thickness of the insulating film is preferably 1000 to 3000 mm. This is because, in the above ridge type semiconductor laser device, in order to cause a difference in refractive index between the AlGaAs active layer large refractive index region 104a and the AlGaAs active layer small refractive index region 104b, the thickness of the insulating film is 1000 mm or more. This is because the thickness of the insulating film needs to be 3000 mm or less in order to prevent the insulating film formed on the side surface of the ridge portion from being peeled off from the side surface of the ridge portion.

  In the above ridge type semiconductor laser element, the insulating film may be made of silicon nitride.

  The manufacturing method of the ridge type semiconductor laser device of the present invention uses a P-CVD method (plasma / chemical vapor deposition method) for forming an insulating film made of silicon nitride in each of the above ridge type semiconductor laser devices. It is said. For this reason, a manufacturing method with good coverage can be realized.

  According to the present invention, the refractive index of the insulating film of the ridge type semiconductor laser device is smaller than the refractive index of the P-type cladding layer, and the difference between the refractive index of the insulating film and the refractive index of the P-type cladding layer is within one. Therefore, there are no severe irregularities in the far field pattern of this ridge type semiconductor laser element other than the peak portion. Therefore, since the ridge type semiconductor laser device of the present invention is formed using an insulating film that can be stably driven by APC and can be formed at low cost, it is possible to perform crystal growth again using the MOCVD method or the like. It is not necessary to cause the increase in manufacturing cost.

  Hereinafter, a ridge type semiconductor laser device according to an embodiment of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
The ridge type semiconductor laser device of the present invention in Embodiment 1 uses an AlGaAs mixed crystal for the active layer, and has the same structure as the conventional ridge type semiconductor laser device shown in FIG. That is, the ridge-type semiconductor laser device according to the first embodiment includes a buffer layer 102 made of N-type GaAs and an N-type cladding layer 103 made of N-type Al _0.5 Ga _0.5 As on a substrate 101 made of N-type GaAs in FIG. , An active layer 104 made of Al _0.13 Ga _0.87 As and a P-type cladding layer 105 made of P-type Al _0.5 Ga _0.5 As and having a ridge 107 projecting upward is stacked in order from the bottom to the top. . A cap layer 106 made of P-type GaAs is disposed on the ridge 107, and the refractive index difference between the ridge 107 and both sides of the ridge 107 and the P-type cladding layer 105 is different from that of the P-type cladding layer 105. The silicon nitride insulating film 108 is covered.

  The silicon nitride forming this insulating film 108 is silicon nitride whose refractive index is smaller than the refractive index of the P-type cladding layer 105 and whose difference from the refractive index of the P-type cladding layer 105 is within one. It is used. In the first embodiment, silicon nitride having a refractive index of 2.8 is used. Since the refractive index of the P-type GaAs forming the P-type cladding layer 105 is about 3.4, the insulating film 108 formed using this silicon nitride has the following: “The refractive index of the insulating film 108 is the P-type cladding layer. And the difference between the refractive index of the insulating film 108 and the refractive index of the P-type cladding layer 105 is within 1 ”.

  A P-side ohmic electrode 110 made of Au—Zn or the like is formed on the cap layer 106. A die-bonding electrode 111 made of Au is formed on the P-side ohmic electrode 110 and outside the insulating film 108. Is formed. Further, an N-side ohmic electrode 112 made of Au—Ge or the like is formed under the substrate 101 made of N-type GaAs, and a wire bond electrode 113 made of Au is further formed thereunder.

  FIG. 4 shows a far-field pattern in the horizontal and transverse modes of the ridge type semiconductor laser device according to the first embodiment having the above structure, and no severe irregularities other than the peak portion are observed. The ripple value in this far field pattern is 5.7%, which satisfies the above-mentioned 10% or less. Therefore, the ridge type semiconductor laser device of Embodiment 1 is configured using the insulating film 108 that can be stably driven by APC and can be formed at low cost, and is formed by MOCVD (metal organic chemical vapor deposition). For example, it is not necessary to re-grow the crystal using a method, etc., so that an increase in manufacturing cost can be suppressed.

FIG. 5 illustrates a method for manufacturing a ridge type semiconductor laser device having the structure of the first embodiment. As a manufacturing method of the ridge type semiconductor laser device having the structure of the first embodiment, in FIG. 5, first, an N-type GaAs buffer layer 102, an N-type Al _0.5 Ga _0.5 As are formed on a wafer-like substrate 101 made of N-type GaAs. A clad layer 103, an Al _0.10 Ga _0.90 As active layer 104, a P-type Al _0.5 Ga _0.5 As clad layer 105, and a P-type GaAs cap layer 106 are sequentially stacked by MOCVD (FIG. 5A).

Next, all of the both sides in the width direction of the P-type GaAs cap layer 106 and the portion of the P-type Al _0.5 Ga _0.5 As cladding layer 105 in the width direction on both sides in a predetermined depth are removed by etching. The ridge portion 107 is formed, and after the ridge portion 107 is formed, nitriding is performed on the P-type GaAs cap layer 106 and the P-type Al _0.5 Ga _0.5 As cladding layer 105 by P-CVD (plasma / chemical vapor deposition). A silicon insulating film 108 is stacked (FIG. 5B).

The thickness of the insulating film 108 formed using silicon nitride is 3000 mm or less in order to prevent film peeling at the interface with the P-type Al _0.5 Ga _0.5 As cladding layer 105 and both sides of the ridge 107. Is desirable. In the ridge type semiconductor laser device, in order to cause a difference in refractive index between the large refractive index region 104a of the AlGaAs active layer and the small refractive index region 104b of the AlGaAs active layer, the thickness of the insulating film 108 is 1000 mm or more. It is known that. Therefore, it is desirable to adjust the thickness of the insulating film 108 in the range of 1000 to 3000 mm. In the first embodiment, the thickness of the insulating film 108 is 2000 mm.

  As a method for forming the insulating film 108, a PVD method (physical vapor deposition method) or a CVD method (chemical vapor deposition method) such as vapor deposition or sputtering can be used, but a P-CVD method with good coverage is preferable.

  After forming the insulating film 108, a photoresist is applied on the insulating film 108 by, for example, a spin coating method to form a photoresist film 109 (FIG. 5C), and ultraviolet light is applied to the photoresist film 109. Development is performed by irradiating light such as photolithography, and only the photoresist film 109 on the cap layer 106 is removed to expose the upper surface of the P-type GaAs cap layer 106.

  In this state, a P-side ohmic electrode 110 made of Au—Zn for ohmic junction is formed (FIG. 5D). Subsequently, the P-side ohmic electrode 110 made of Au—Zn is left only on the P-type GaAs cap layer 106 exposed by removing the photoresist film 109 (FIG. 5E).

  Thereafter, an N-side ohmic electrode 112 such as Au—Ge is formed on the lower surface of the substrate 101 made of N-type GaAs. Finally, a die bond made of Au or the like is formed on the upper surface of the P-side ohmic electrode 110 and outside the insulating film 108. An electrode 111 is formed, and a wire bond electrode 113 is formed under the N-side ohmic electrode 112 (FIG. 5 (f)).

  In the ridge type semiconductor laser device of the first embodiment, silicon nitride is used for forming the insulating film 108, but silicon oxide may be used.

  Next, ridge type semiconductor laser elements having the same structure as the ridge type semiconductor laser element of Embodiment 1 are manufactured using various silicon nitrides having different refractive index values, and the far field of these ridge type semiconductor laser elements is manufactured. The graph of FIG. 6 shows the correlation with the refractive index of the insulating film 108 by measuring the ripple value of the pattern. According to FIG. 6, the refractive index is smaller than the refractive index of the P-type cladding layer of about 3.4, the difference is 1 or less, and the ripple value 10 necessary for stably APC driving the semiconductor laser. In order to realize% or less, the refractive index of silicon nitride may be 2.4 to 3.4.

<Embodiment 2>
The ridge type semiconductor laser device according to the second embodiment uses an AlGaInP mixed crystal for the active layer, and its structure is shown in FIG. The structure of the ridge type semiconductor laser device in the second embodiment is substantially the same as that of the conventional ridge type semiconductor laser device shown in FIG. That is, the ridge type semiconductor laser device according to the second embodiment includes a buffer layer 202 made of N-type Ga _0.5 In _0.5 P, an N-type (Al _0.7 Ga _0.3 ) _0.5 In on the substrate 201 made of N-type GaAs in FIG. _A cladding layer 203 made of _0.5 P, an active layer 204 made of Ga _0.5 In _0.5 P, and a P-type cladding layer having a ridge portion 207 made of P-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and projecting upward. 205 are sequentially stacked. An intermediate layer 214 made of P-type Ga _0.5 In _0.5 P and a cap layer 206 made of P-type GaAs are disposed on the ridge portion 207, and both sides of the ridge portion 207 and the P-type are formed. The clad layer 205 is covered with an insulating film 208 of silicon nitride having a refractive index difference from that of the P-type clad layer 205.

The silicon nitride forming the insulating film 208 is silicon nitride whose refractive index is smaller than the refractive index of the P-type cladding layer 205 and whose difference from the refractive index of the P-type cladding layer 205 is within one. It is used. In the second embodiment, as in the first embodiment, silicon nitride having a refractive index of 2.8 is used. Since the refractive index of P-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P forming the P-type cladding layer 205 is about 3.3, the insulating film 208 formed using this silicon nitride is “insulating film”. 208, the refractive index of 208 is smaller than the refractive index of the P-type cladding layer 205, and the difference between the refractive index of the insulating film 208 and the refractive index of the P-type cladding layer 205 is within one.

  A P-side ohmic electrode 210 made of Au—Zn or the like is formed on the cap layer 206. A die-bonding electrode 211 made of Au is formed on the P-side ohmic electrode 210 and outside the insulating film 208. Is formed. An N-side ohmic electrode 212 made of Au-Ge or the like is formed under the substrate 201 made of N-type GaAs, and a wire bond electrode 213 made of Au is further formed thereunder.

  Although not shown in the ridge type semiconductor laser device in the second embodiment, a horizontal field mode far field pattern similar to that in the first embodiment is obtained. Also in this far field pattern, No severe irregularities other than the peak were observed.

  The manufacturing method of the ridge type semiconductor laser device having the structure of the second embodiment is substantially the same as the manufacturing method of the ridge type semiconductor laser device having the structure of the first embodiment. Therefore, it is desirable to adjust the film thickness of the insulating film 208 in the range of 1000 to 3000 mm as in the first embodiment. As a method for forming the insulating film 208, a PVD method such as vapor deposition or sputtering or a CVD method can be used as in the first embodiment, but a P-CVD method with good coverage is preferable.

  Similarly to the first embodiment, a ridge type semiconductor laser device having the same structure as the ridge type semiconductor laser device of the second embodiment is manufactured using various silicon nitrides having different refractive index values, and an insulating film is formed. The correlation between the refractive index of 208 and the ripple value of the horizontal field mode far field pattern was determined. According to the result (not shown), the refractive index is smaller than the refractive index of the P-type cladding layer of about 3.3, the difference is 1 or less, and the semiconductor laser is stably driven by APC. In order to realize a ripple value of 10% or less necessary for the above, the refractive index of silicon nitride may be set to 2.3 to 3.3.

FIG. 2 is a structural diagram of a ridge type semiconductor laser device in Embodiment 1 and a ridge type semiconductor laser device in a conventional example. It is explanatory drawing of a far field pattern. (a), (b) is a far field pattern of the conventional ridge type semiconductor laser element. 2 is a far field pattern of a ridge type semiconductor laser device according to Embodiment 1. (a)-(f) is the manufacturing method of the ridge type semiconductor laser element of Embodiment 1. FIG. 3 is a graph showing a correlation between a refractive index of an insulating film and a ripple in the ridge type semiconductor laser device in Embodiment 1. FIG. 5 is a structural diagram of a ridge type semiconductor laser element in Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Ridge-type semiconductor laser element 101 NGaAs substrate 102 NGaAs buffer layer 103 N-type AlGaAs cladding layer 104 AlGaAs active layer 104a AlGaAs active layer large refractive index region 104b AlGaAs active layer small refractive index region 105 P-type AlGaAs cladding layer 106 P-type GaAs cap Layer 107 Ridge part 108 Insulating film 109 Photoresist film 110 P-type ohmic electrode 111 Die bond electrode 112 N type ohmic electrode 113 Wire bond electrode 120 Light emitting region 121 Laser beam 122 Horizontal transverse mode far field pattern 200 Ridge type semiconductor laser device 201 N-type GaAs substrate 202 N-type GaInP buffer layer 203 N-type AlGaInP cladding layer 204 GaInP active layer 204a GaInP active layer large refractive index region 204b GaInP active layer small refractive index region 205 P-type AlGaInP cladding layer 206 P-type G aAs cap layer 207 Ridge portion 208 Insulating film 209 Photoresist film 210 P-type ohmic electrode 211 Die-bonding electrode 212 N-type ohmic electrode 213 Wire-bonding electrode 214 P-type GaInP intermediate layer

Claims (6)

At least an N-type cladding layer, an active layer, and a P-type cladding layer are sequentially stacked from the bottom to the top, and a ridge portion having a shape in which a part of the P-type cladding layer protrudes upward is formed on the P-type cladding layer. In addition, the side surface of the ridge portion and the upper surface of the P-type cladding layer on which the ridge portion is not formed have a structure covered with an insulating film, and the ridge portion is interposed through the P-type cladding layer. The structure causes a refractive index difference between a large refractive index region that is a part of the active layer that is in contact with a small refractive index region that is a part of the active layer that is in contact with the insulating film via the P-type cladding layer. In addition, in the ridge type semiconductor laser device in which the optical confinement in the lateral direction is made by the refractive index difference,
A ridge type wherein the refractive index of the insulating film is smaller than the refractive index of the P-type cladding layer, and the difference between the refractive index of the insulating film and the refractive index of the P-type cladding layer is within one. Semiconductor laser element.   2. A ridge type semiconductor laser device according to claim 1, wherein the active layer is formed of an AlGaAs mixed crystal, and the refractive index of the insulating film is 2.4 to 3.4.   2. The ridge type semiconductor laser device according to claim 1, wherein the active layer is formed of an AlGaInP-based mixed crystal, and the refractive index of the insulating film is 2.3 to 3.3.   4. The ridge type semiconductor laser device according to claim 1, wherein the insulating film has a thickness of 1000 to 3000 mm. 5.   The ridge-type semiconductor laser device according to claim 1, wherein the insulating film is made of silicon nitride. A method of manufacturing a ridge type semiconductor laser device according to claim 5,
A method of manufacturing a ridge type semiconductor laser device, wherein a plasma CVD method is used to form the insulating film made of silicon nitride.

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